Thermoplastic sheets have provided effective and relatively light weight covers for a wide variety of uses including cargo and container covers, ground covers, and temporary building covers. The thermoplastic sheets are waterproof, and can include additives for ultraviolet protection from degradation in sunlight, flame retardants, and coloring pigments depending on the intended use.
Reinforced thermoplastic laminates have been made previously with a reinforcing grid between two sheets of thermoplastic to enhance the physical performance of the product. The reinforcing grid is typically a scrim of woven or nonwoven fabric. In some reinforced thermoplastic laminates, the thermoplastic sheets are bonded to each other in between the grid pattern of the reinforcing material. Thermoplastics with different melt characteristics for laminating the sheets around the grid also have been utilized. Although the heat sealing provides good bonding around the reinforcing grid, these reinforced thermoplastic laminates are nonetheless susceptible to tearing as shown in FIG. 6.
Another type of reinforced thermoplastic laminate includes a layer of flexible adhesive in between the thermoplastic sheets. The grid is disposed within the layer of flexible adhesive. The flexible adhesive allows the scrim to slip in between the thermoplastic sheets, thereby providing good tear resistance. The enhanced tear resistance of the laminate results from the tendency of the strands of the scrim to slide together without breaking within the laminate when a tear is pulled. However, laminates with adhesives, although having improved tear resistance, can delaminate as shown in FIG. 7. These laminates are particularly susceptible to outdoors delamination due to water or heat sensitivity. Therefore, reinforced thermoplastic laminates without adhesives have enhanced lamination strength, but diminished tear resistance, while those with adhesives have enhanced tear resistance, but diminished lamination strength.